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This paper demonstrates a much higher incidence of dementia in PD patients than previously reported. This might reflect the disease mechanisms we investigate in our current paper, Giasson et al., 2003. The percentage of patients with Parkinson’s disease who will also develop dementia is unknown. While there are reports of the prevalence of dementia among PD patients, none of the longitudinal studies conducted have included a representative PD patient sample. Longitudinal studies can give us an estimate of the proportion of patients with PD who will eventually develop dementia.

This prospective study followed 224 diagnosed PD patients drawn from among 220,000 residents of western Norway, who were free of dementia at baseline. Patients received two clinical examinations by a neurologist at study onset. Patients and their caregivers were interviewed to establish a history of their disease. Collected data included demographics, drug therapy information, history of hallucinations while on anti-PD drugs, motor symptoms information, laboratory tests. DSM-III-R criteria, plus three rating scales for cognitive impairment served to diagnose dementia. During follow-up examinations four and eight years later, two physicians evaluated study participants for dementia using cognitive screening, neuropsychological testing, and a clinical interview.

The control group consisted of 3,295 residents of Odense, Denmark, who were aged 65 to 84 and did not have PD. For this group, a diagnosis of dementia was made and follow-up evaluations were conducted two and five years after the baseline evaluation.

In the PD group, 139 participants were evaluated at the four-year follow up, and 87 at eight years. At baseline, 26 percent (51 cases) of the PD study subject group were diagnosed with dementia; 43 additional cases were diagnosed four years later, and 28 new cases were identified at the eight-year point, totaling 122 cases of dementia among the PD group. This means a prevalence for dementia among PD patients of 78.2 percent (95 percent CI, 71.1-84.0 percent) at the eight-year follow-up, whereas the five-year prevalence in the control group was 18.5 percent. Logistic regression analysis identified hallucinations prior to baseline examination and mixed tremor/akinetic PD as significant predictors of dementia. The extended periods of time between evaluations lead to loss of subjects at each follow-up point, suggesting that dementia rates among PD patients may be even higher than recorded here, the authors note. This potential consequence of Parkinson’s should be addressed. See also Wilson et al., 2003.